1. Field of the Invention
The present invention relates to a method and an apparatus for evaluating the service life of a secondary battery and a computer-readable recorded medium containing a program for executing a secondary battery evaluation process.
2. Description of the Related Art
Secondary batteries are used as a power source in information processing devices and portable information processing terminals with or without the charging section. Because such secondary batteries have a finite service life depending on the of type of battery, it is essential to be able to forecast the service life so that service interruption would not be experienced. For portable information devices and personal computers based on volatile memory, it is especially important to maintain a full power source because the power failure leads to a loss of information stored in the volatile memory.
An example of battery life evaluation apparatuses for evaluating the service life of batteries is disclosed in a Japanese Patent Application, First Publication, Hei7-201370.
This apparatus is designed to evaluate the service life of a battery by recording charging data, such as charging current, charging time, voltage at charge startup, voltage at charge completion and the number of charges performed, in a charging data storage section 1, and recording the basic operating parameters of the secondary battery in a basic parameter storage section 2, and the stored data in the charge data storage section 1 and the basis parameter storage section 2 are sent to and compared in an evaluation section 3.
Another example of battery life evaluation apparatus is disclosed in a Japanese Patent Application, First Publication, Hei7-17966.
This apparatus evaluates service life of storage batteries installed in vehicles, and is designed to evaluate a storage battery 1 in an electric car. In this apparatus, battery usage data such as properties of the battery 1, conditions of usage, historical data and others are recorded in RAM 8-6, and for evaluation of battery life, the battery 1 is removed from the car and is connected to an external computer, with an intervening interface circuit 8-5, which analyzes the recorded chronological usage data together with the historical data recorded in RAM 8-6 through the interface circuit 8-5. The apparatus is then returned to the electric car, and at suitable intervals, the data recorded in RAM 8-6 (such as battery properties, conditions of usage, historical data and others) are accessed and compared with real-time data obtained by way of the interface circuit 8-6 so as to evaluate the extent of degradation experienced by the storage battery 1, in other words, to evaluate the remaining service life of the battery 1.
Therefore, in both of these apparatuses that are disclosed, evaluation is performed according to chronological historical data of secondary battery or storage battery.
However, in both of these battery life evaluation apparatuses, although the service life is supposed to be evaluated according to chronological historical data, many of the essential factors necessary for accurate evaluation of secondary batteries and storage batteries are not being considered in evaluating the service life of the secondary batteries and storage batteries, resulting that accurate determination of battery service life cannot be obtained.
It is an object of the present invention to provide a method and an apparatus for providing accurate data on service life and useable time remaining in a secondary battery for use in portable terminal devices, and to provide a recorded medium containing service life evaluation program for a secondary battery.
To resolve the problems outline above, the present invention provides a first aspect of the invention in a method for determining a service life of a secondary battery subjected to repeated charging/discharging cycles; comprising the steps of: storing, in a memory device, pre-measured values of an index related to decrements in service life of the battery, which is fully charged after each discharge event during a charging/discharging cycle, to correspond to discharged amounts produced during charging/discharging cycles experienced by the battery during the respective charging/discharging cycles; computing a discharged amount after each charging/discharging cycle; obtaining an index to correspond to the discharged amount from the memory device; computing a service life remaining after the current cycle of charging/discharging according to a maximum service life of the battery and the values of the index obtained in individual charging/discharging cycles, including the current charging/discharging cycle; and determining whether or not the remaining service life computed is less than a pre-determined reference value, and deeming that the battery has reached an end of the service life when the computed value is less than the reference value.
A second aspect of the invention relates to a method for determining a service life of a secondary subjected to repeated charging and discharging processes, comprising the steps of: storing, in a memory device, pre-measured values of an index related to decrements in service life of the battery and various amounts of charges and discharges produced in charging/discharging cycles corresponding to the charged and discharged amounts experienced by the battery during the respective charging/discharging cycles; computing a charged amount and a discharged amount after each cycle of charging/discharging; obtaining an index to correspond to the computed charged amount and the computed discharged amount with reference to the memory device; computing a service life remaining after the current cycle of charging/discharging according to a maximum service life of the battery and the values of the index obtained in individual charging/discharging cycles, including the current charging/discharging cycle; and determining whether or not the remaining service life computed is less than a pre-determined reference value, and deeming that the battery has reached an end of the service life when the computed service life is less than the reference value.
A third aspect of the invention relates to a method for determining a useable time for one additional use, after a current cycle of charging/discharging of a secondary battery subjected to repeated cycles of charging/discharging, comprising the steps of: computing a service life of the battery remaining after the current cycle of charging/discharging of the battery; computing an average amount of consumed service life by dividing a cumulative value of consumed service life of individual cycles from a first cycle to the current cycle of charging/discharging by a number of cycles of charging/discharging; computing an average use time of the battery from the first cycle to the current cycle; and computing a useable time for one additional use of the battery after the current cycle of charging/discharging, according to the remaining service life computed, the average amount of consumed service life, and the average use time of the battery.
A fourth aspect of the invention relates to the method according to claim 3, wherein the remaining service life of the battery is obtained by subtracting a cumulative consumed service life including the current cycle of charging/discharging from the maximum service life of the battery.
A fifth aspect of the invention relates to the method according to claim 3 or 4, wherein the remaining service life of the battery is obtained by: storing, in a memory device, pre-measured values of an index related to decrements in service life of the battery, which is fully charged after each discharge event during a charging/discharging cycle, to correspond to discharged amounts produced during charging/discharging cycles experienced by the battery during the respective charging/discharging cycles; computing a first cumulative discharged amount from individual cycles of charging/discharging including a preceding cycle of charging/discharging of the battery; obtaining a value of the index with reference to the memory device to correspond to the first cumulative discharged amount from individual cycles of charging/discharging including the preceding cycle; computing a first service life of the battery remaining after the preceding cycle of charging/discharging, according to the maximum service life of the battery and the values of the index obtained from individual cycles of charging/discharging including the preceding cycle of charging/discharging of the battery; computing a second cumulative discharged amount from individual cycles of charging/discharging including a current cycle of charging/discharging of the battery; obtaining another value of the index with reference to the memory device to correspond to the second cumulative discharged amount from individual cycles of charging/discharging including the current cycle; computing a second service life of the battery remaining after the current cycle of charging/discharging, according to the maximum service life of the battery and the values of the index obtained from individual cycles of charging/discharging including the current cycle of charging/discharging of the battery; and obtaining the remaining service life of the battery by subtracting the first cumulative service life from the second cumulative service life.
A sixth aspect of the invention relates to the method according to claim 5 or 6, wherein the remaining service life of the battery is obtained by: storing, in a memory device, pre-measured values of an index related to decrements in service life of the battery and various amounts of charges and discharges produced in charging/discharging cycles corresponding to the charged and discharged amounts experienced by the battery during the respective charging/discharging cycles; computing a charged amount and a discharged amount after each cycle of charging/discharging; computing a first cumulative charged amount and a first cumulative discharged amount from individual cycles of charging/discharging including a preceding cycle of charging/discharging of the battery; obtaining an index with reference to the memory device to correspond to the first cumulative charged amount and the first cumulative discharged amount from individual cycles of charging/discharging including the preceding cycle; computing a first service life of the battery remaining after the preceding cycle of charging/discharging, according to the maximum service life of the battery and the values of the index obtained from individual cycles of charging/discharging including the preceding cycle of charging/discharging of the battery; computing a second cumulative charged amount and the second cumulative discharged amount from individual cycles of charging/discharging including a current cycle of charging/discharging of the battery; obtaining an index with reference to the memory device to correspond to the second cumulative charged amount and the second cumulative discharged amount from individual cycles of charging/discharging including the current cycle; computing a second service life of the battery remaining after the current cycle of charging/discharging, according to the maximum service life of the battery and the values of the index obtained for individual cycles of charging/discharging including the current cycle of charging/discharging of the battery; and obtaining the remaining service life of the battery by subtracting the first service life from the second service life.
A seventh aspect of the invention relates to an apparatus for determining a service life of a secondary battery subjected to repeated cycles of charging/discharging of the battery, comprising: first memory unit storing, in a memory device, pre-measured values of an index related to decrements in service life of the battery, which is fully charged after each discharge event during a charging/discharging cycle, to correspond to discharged amounts produced during charging/discharging cycles experienced by the battery during the respective charging/discharging cycles; first discharged amount computation unit which computes a discharged amount for each cycle of charging/discharging; first index obtaining unit which obtains an index to correspond to a discharged amount computed by the first discharged amount computation unit with reference to the first memory unit; computing a service life remaining after the current cycle of charging/discharging according to a maximum service life of the battery and the values of the index obtained in individual charging/discharging cycles, including the index obtained in the current charging/discharging cycle; and first determination unit which determines whether or not the remaining service life computed is less than a pre-determined reference value, and deeming that the battery has reached an end of the service life when the computed service life is less than the reference value.
An eighth aspect of the invention relates to an apparatus for determining a service life of a secondary battery subjected to repeated cycles of charging/discharging of the battery, comprising: second memory unit which stores, in a memory device, pre-measured values of an index related to decrements in service life of the battery and various amounts of charges and discharges produced in charging/discharging cycles corresponding to the charged and discharged amounts experienced by the battery during the respective charging/discharging cycles; computing a charged amount and a discharged amount after each cycle of charging/discharging; first charged/discharged amount computation unit which computes a charged amount and a discharged amount for each cycle of charging/discharging; second index obtaining unit which obtains an index to correspond to a charged amount and a discharged amount computed by the first charged/discharged amount computation unit with reference to the second memory unit; second service life computation unit which computes a remaining service life of the battery after the current cycle of charging/discharging according to the maximum service life of the battery and the index obtained by the second index obtaining unit from individual cycles of charging/discharging including current cycle of charging/discharging; and second determination unit which determines whether or not the remaining service life computed is less than a pre-determined reference value, and deeming that the battery has reached an end of the service life when the computed service life is less than the reference value.
A ninth aspect of the invention relates to an apparatus for determining a useable time for one additional use, after a current cycle of charging/discharging of a secondary battery subjected to repeated cycles of charging/discharging, comprising: service life computation unit which computes a service life of the battery remaining after the current cycle of charging/discharging of the battery; average service life computation unit which computes an average amount of consumed service life by dividing a cumulative value of consumed service life of individual cycles from a first cycle to the current cycle of charging/discharging by a number of cycles of charging/discharging; average use time computing unit which computes an average use time of the battery from the first cycle to the current cycle; and useable time computation unit which computes a useable time for one additional use of the battery after the current cycle of charging/discharging, according to the remaining service life computed, the average amount of consumed service life, and the average use time of the battery.
A tenth aspect of the invention relates to the apparatus according to claim 9, wherein the remaining service life computed by the remaining service life computation unit is obtained by subtracting from the maximum service life of the battery a cumulative consumed service life in individual cycles of charging/discharging from the first use to the current use.
An eleventh aspect of the invention relates to the apparatus according to claim 9 or 10, wherein the service life decrement computation unit comprises: third memory unit which stores, in a memory device, pre-measured values of an index related to decrements in service life of the battery, which is fully charged after each discharge event during a charging/discharging cycle, to correspond to discharged amounts produced during charging/discharging cycles experienced by the battery during the respective charging/discharging cycles; second discharged amount computation unit which computes a discharged amount for each cycle of charging/discharging; third index obtaining unit which obtains an index to correspond to a discharged amount computed by the second discharged amount computation unit with reference to the third memory unit; and first differential outputting unit which outputs a difference between a service life remaining in the battery after the preceding cycle of charging/discharging computed according to the maximum service life of the battery and the values of the index obtained by the third index obtaining unit for individual cycles of charging/discharging including the preceding cycle of discharge, on the one hand, and a service life remaining in the battery after the current cycle of charging/discharging computed according to the maximum service life of the battery and the values of the index obtained by the third index obtaining unit for individual cycles of charging/discharging including the current cycle of discharge, on the other.
A twelfth aspect of the invention relates to the useable time computation apparatus according claim 9 or 10, wherein the service life decrement computation unit comprises: fourth memory unit which stores pre-measured values of an index related to decrements in service life of the battery and various amounts of charges and discharges produced in charging/discharging cycles corresponding to the charged and discharged amounts experienced by the battery during the respective charging/ discharging cycles; computing a charged amount and a discharged amount after each cycle of charging/discharging; second discharged amount computation unit which computes a discharged amount for each cycle of charging/discharging; fourth index obtaining unit which obtains an index to correspond to a discharged amount computed by the second discharged amount computation unit with reference to the fourth memory unit; and second differential outputting unit which outputs a difference between a service life remaining in the battery after the preceding cycle of charging/discharging computed according to the maximum service life of the battery and the values of the index obtained by the fourth index obtaining unit for individual cycles of charging/discharging including the preceding cycle of discharge, on the one hand, and a service life remaining in the battery after the current cycle of charging/discharging computed according to the maximum service life of the battery and the values of the index obtained by the fourth index obtaining unit for individual cycles of charging/discharging including the current cycle of discharge, on the other.
A final aspect of the invention relates to a computer-readable recorded medium containing a program for determining a service life of a secondary battery according to an aspect of the invention disclosed in claims 1, 2, 3, 7, 8, and 9.
Accordingly, because the service life of the battery is evaluated by following a process, in which a discharged amount is computed each time the secondary battery used, a service life degradation index is obtained to correspond to the discharged amount computed, so that the service life can be computed according to the maximum life of the battery and the values of the degradation index obtained for each prior uses of the battery to the current use, and the service life of the battery is determined according to whether the computed service life is longer or shorter than a reference value, and therefore, the method enables to evaluate the service life of the battery without raising the cost of the portable terminal, thereby enabling to more accurately forecast the remaining life of the spare battery.
Also, because the service life of the battery is evaluated by following the process, in which the amounts of charges and discharges preceding the current use are computed each time the secondary battery used, a service life degradation index is obtained to correspond to the computed charged and discharged amounts, so that a service life after the current use can be computed according to the maximum life of the battery and the values of the degradation index obtained for each prior uses of the battery, and the service life of the battery is determined according to whether the computed service life is longer or shorter than a reference value, and therefore, the method enables to evaluate the service life of the battery, thereby enabling to more accurately forecast the remaining life of the spare battery.
Also, because the service life of the battery is evaluated by following the process, in which service life of the battery remaining including the current use, the average consumed service life including the current use and the average use time including the current use are computed, and a useable time remaining after the current use is reported according to the computed values of the remaining service life, average consumed service life and average use time, thereby enabling to report the useable time remaining in the battery after each use of the battery.
Therefore, it is possible to report the service life as well as the useable time of the battery so that the loss of important information contained in the volatile memory in the portable terminal, caused by inattention to the life of the spare battery, can be prevented even more completely, thereby contributing significantly to maintain smooth operation of the portable information processing device.